The mobile platform measures 30x16x14 (L/W/H) Inches. I think this is the bare minimum to carry an SLR/Lens combo of this size and weight. The ideal device would actually be an R/C replica of a Main Battle Tank - and if I could find one, that would be my choice.

As pointed out by Ka Mastah Romy, I need to have a mechanism that will allow me to raise or lower the lens angle, and not just swivel the camera. Also, the battery lasts only a maximum of 30 minutes for this prototype, so a higher-capacity unit is crucial.

The contraption will easily travel on flat, semi-rough surfaces, but I would not recommend a tight turn when in full gallop as the 450D/400mm Lens combo raises the rig's center of gravity - making it somewhat top-heavy.

Also, I'd like to be clear that I made this because I think it's a FUN project, that may or may not be good enough for its intended purpose, but it has the potential, anyway.